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<h3><a name="SECTION0016342000000000000000"></a><a name="optparse-how-callbacks-called"></a>
<br>
14.3.4.2 How callbacks are called
</h3>

<p>
All callbacks are called as follows:
<div class="verbatim"><pre>
func(option, opt_str, value, parser, *args, **kwargs)
</pre></div>

<p>
where
<dl>
<dt><strong><code>option</code></strong></dt>
<dd>is the Option instance that's calling the callback
</dd>
<dt><strong><code>opt_str</code></strong></dt>
<dd>is the option string seen on the command-line that's triggering the
callback.  (If an abbreviated long option was used, <code>opt_str</code> will
be the full, canonical option string--e.g. if the user puts
<code>"-foo"</code> on the command-line as an abbreviation for
<code>"-foobar"</code>, then <code>opt_str</code> will be <code>"-foobar"</code>.)
</dd>
<dt><strong><code>value</code></strong></dt>
<dd>is the argument to this option seen on the command-line.  <tt class="module">optparse</tt> will
only expect an argument if <tt class="member">type</tt> is set; the type of <code>value</code>
will be the type implied by the option's type.  If <tt class="member">type</tt> for this
option is <code>None</code> (no argument expected), then <code>value</code> will be
<code>None</code>.  If <code>nargs</code> &gt; 1, <code>value</code> will be a tuple of values of
the appropriate type.
</dd>
<dt><strong><code>parser</code></strong></dt>
<dd>is the OptionParser instance driving the whole thing, mainly
useful because you can access some other interesting data through
its instance attributes:
<dl>
<dt><strong><code>parser.largs</code></strong></dt>
<dd>the current list of leftover arguments, ie. arguments that have
been consumed but are neither options nor option arguments.
Feel free to modify <code>parser.largs</code>, e.g. by adding more
arguments to it.  (This list will become <code>args</code>, the second
return value of <tt class="method">parse_args()</tt>.)
</dd>
<dt><strong><code>parser.rargs</code></strong></dt>
<dd>the current list of remaining arguments, ie. with <code>opt_str</code> and
<code>value</code> (if applicable) removed, and only the arguments
following them still there.  Feel free to modify
<code>parser.rargs</code>, e.g. by consuming more arguments.
</dd>
<dt><strong><code>parser.values</code></strong></dt>
<dd>the object where option values are by default stored (an
instance of optparse.OptionValues).  This lets callbacks use the
same mechanism as the rest of <tt class="module">optparse</tt> for storing option values;
you don't need to mess around with globals or closures.  You can
also access or modify the value(s) of any options already
encountered on the command-line.
</dd>
</dl>
</dd>
<dt><strong><code>args</code></strong></dt>
<dd>is a tuple of arbitrary positional arguments supplied via the
<code>callback_args</code> option attribute.
</dd>
<dt><strong><code>kwargs</code></strong></dt>
<dd>is a dictionary of arbitrary keyword arguments supplied via
<code>callback_kwargs</code>.
</dd>
</dl>

<p>

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